Capitalization and Short-Term Borrowings - Schedule of Long-Term Debt (Details) - USD ($) $ in Thousands		12 Months Ended
		Sep. 30, 2025	Sep. 30, 2024	Mar. 06, 2025	Feb. 19, 2025
Debt Instrument [Line Items]
Total Long-Term Debt		$ 2,700,000	$ 2,700,000
Less Unamortized Discount and Debt Issuance Costs		17,139	11,757
Less Current Portion	[1]	300,000	500,000
Long-Term Debt, Net of Current Portion and Unamortized Discount and Debt Issuance Costs		2,382,861	2,188,243
5.20% Notes Due July 2025
Debt Instrument [Line Items]
Long-term debt, face amount				$ 450,000
Less Current Portion			$ 450,000
Long-term debt, interest rate			5.20%	5.20%
7.38% due June 2025
Debt Instrument [Line Items]
Medium-Term Notes	[2]	$ 0	$ 50,000
Less Current Portion			$ 50,000
Long-term debt, interest rate		7.38%	7.38%
2.95% to 5.95% due October 2026 to March 2035
Debt Instrument [Line Items]
Notes	[2],[3],[4]	$ 2,400,000	$ 2,350,000
Percentage of principal amount		101.00%	101.00%
2.95% to 5.95% due October 2026 to March 2035 | Minimum
Debt Instrument [Line Items]
Long-term debt, interest rate		2.95%	2.95%
2.95% to 5.95% due October 2026 to March 2035 | Maximum
Debt Instrument [Line Items]
Long-term debt, interest rate		5.95%	5.95%
Term Loan Agreement
Debt Instrument [Line Items]
Long-term debt, face amount	[5]	$ 300,000	$ 300,000
Less Current Portion		$ 300,000
Long-term debt, weighted average variable interest rate		5.62%	6.71%
Term Loan Agreement | Rate through December 2025
Debt Instrument [Line Items]
Long-term debt, variable interest rate		5.43%
4.75% Notes Due September 1, 2028
Debt Instrument [Line Items]
Long-term debt, face amount		$ 300,000
Long-term debt, interest rate		4.75%
Maximum interest rate adjustment		2.00%
3.95% Notes Due September 15, 2027
Debt Instrument [Line Items]
Long-term debt, face amount		$ 300,000
Long-term debt, interest rate		3.95%
Maximum interest rate adjustment		2.00%
2.95% Notes Due March 1, 2031
Debt Instrument [Line Items]
Long-term debt, face amount		$ 500,000
Long-term debt, interest rate		2.95%
Maximum interest rate adjustment		2.00%
5.50% Notes Due October 1, 2026
Debt Instrument [Line Items]
Long-term debt, face amount		$ 300,000
Long-term debt, interest rate		5.50%
Maximum interest rate adjustment		2.00%
5.50% Notes Due March 15, 2030
Debt Instrument [Line Items]
Long-term debt, face amount		$ 500,000			$ 500,000
Long-term debt, interest rate		5.50%			5.50%
Maximum interest rate adjustment		2.00%
5.50% Notes Due March 15, 2030 | Maximum
Debt Instrument [Line Items]
Long-term debt, interest rate		7.50%
5.95% Notes Due March 15, 2035
Debt Instrument [Line Items]
Long-term debt, face amount		$ 500,000			$ 500,000
Long-term debt, interest rate		5.95%			5.95%
Maximum interest rate adjustment		2.00%
5.95% Notes Due March 15, 2035 | Maximum
Debt Instrument [Line Items]
Long-term debt, interest rate		7.95%

[1] Current Portion of Long-Term Debt at September 30, 2025 consisted of a $300.0 million long-term delayed draw term loan that matures in February 2026. Current Portion of Long-Term Debt at September 30, 2024 consisted of $50.0 million of 7.38% medium-term notes and $450.0 million of 5.20% notes.

[2] The Medium-Term Notes and Notes are unsecured.

[3] The holders of these notes may require the Company to repurchase their notes at a price equal to 101% of the principal amount in the event of both a change in control and a ratings downgrade to a rating below investment grade.

[4] The interest rate payable on $300.0 million of 4.75% notes, $300.0 million of 3.95% notes, $500.0 million of 2.95% notes and $300.0 million of 5.50% notes will be subject to adjustment from time to time, with a maximum of 2.00%, if certain change of control events involving a material subsidiary result in a downgrade of the credit rating assigned to the notes to below investment grade (or if the credit rating assigned to the notes is subsequently upgraded). The interest rate payable on $500.0 million of 5.50% notes and $500.0 million of 5.95% notes will be subject to adjustment from time to time, with a maximum adjustment of 2.00%, such that the coupon will not exceed 7.50% on the 5.50% notes and 7.95% on the 5.95% notes, if certain change in control events involving a material subsidiary result in a downgrade of the credit rating assigned to the notes to a rating below investment grade. A downgrade with a resulting increase to the coupon does not preclude the coupon from returning to its original rate if the Company’s credit rating is subsequently upgraded.

[5] The interest rate on the delayed draw term loan, which is based on a weighted average SOFR interest rate, was 5.62% and 6.71% as of September 30, 2025 and September 30, 2024, respectively. The current weighted average locked-in interest rate is 5.43% until mid-December 2025.